linux网络编程epoll_loop

刺骨的言语ヽ痛彻心扉 2022-12-02 00:56 172阅读 0赞

# linux网络编程epoll\_loop #

# 重要函数 #

## recv函数和send函数 ##

### recv ###

函数

ssize_t recv(int __fd, void *__buf, size_t __n, int __flags)

说明

Read N bytes into BUF from **socket FD**.  
Returns the number read or -1 for errors.

This function is a cancellation point and therefore not marked with \_\_THROW.

### send ###

函数

ssize_t send(int __fd, const void *__buf, size_t __n, int __flags)

说明  
Send N bytes of BUF to **socket FD**. Returns the number sent or -1.

This function is a cancellation point and therefore not marked with \_\_THROW.

## epoll\_create、epoll\_ctl和epoll\_wait函数 ##

### epoll\_create ###

epoll_create - open an epoll file descriptor
           
           On success, these system calls return a nonnegative file descriptor.  
           On error, -1 is returned, and errno is set to indicate the error.

### epoll\_ctl ###

epoll_ctl - control interface for an epoll file descriptor
           
           When successful, epoll_ctl() returns zero.  
           When an error occurs, epoll_ctl() returns -1 and errno is set appropriately.

## epoll\_wait ##

epoll_wait, epoll_pwait - wait for an I/O event on an epoll file descriptor
           
           When  successful,  epoll_wait() returns the number of file descriptors ready for the requested I/O, or zero if no file descriptor became ready during the requested timeout milliseconds.  
           When an error occurs, epoll_wait() returns -1 and errno is set appropriately.

具体可以看[linux并发服务器epoll][linux_epoll]。

# 自定义结构体 #

结构体`struct myevent_s`。

struct myevent_s { 
        int fd;                                                 //要监听的文件描述符
        int events;                                             //对应的监听事件
        void *arg;                                              //泛型参数
        void (*call_back)(int fd, int events, void *arg);       //回调函数
        int status;                                             //是否在监听:1->在红黑树上(监听), 0->不在(不监听)
        char buf[BUFLEN];
        int len;
        long last_active;                                       //记录每次加入红黑树 g_efd 的时间值
    };

## 关系图 ##

![在这里插入图片描述][20200828194209193.jpg]

# epoll 模型 #

在server - >创建树的根节点-> 在树上添加需要监听的节点->监听读事件->有返回-> 通信->epoll\_wait

在server - >创建树的根节点-> 在树上添加需要监听的节点->监听读事件->有返回-> 通信(接收数据)->将这个fd从树上删除->监听写事件->写操作->fd从树上摘下来->监听fd的读事件->epoll\_wait

# epoll基于非阻塞I/O事件驱动 #

/* * epoll基于非阻塞I/O事件驱动 */
    #include <stdio.h>
    #include <sys/socket.h>
    #include <sys/epoll.h>
    #include <arpa/inet.h>
    #include <fcntl.h>
    #include <unistd.h>
    #include <errno.h>
    #include <string.h>
    #include <stdlib.h>
    #include <time.h>
    
    #define MAX_EVENTS 1024 //监听上限数
    #define BUFLEN 4096
    #define SERV_PORT 8080
    
    void recvdata(int fd, int events, void *arg);
    void senddata(int fd, int events, void *arg);
    
    /* 描述就绪文件描述符相关信息 */
    
    struct myevent_s { 
        int fd;                                                 //要监听的文件描述符
        int events;                                             //对应的监听事件
        void *arg;                                              //泛型参数
        void (*call_back)(int fd, int events, void *arg);       //回调函数
        int status;                                             //是否在监听:1->在红黑树上(监听), 0->不在(不监听)
        char buf[BUFLEN];
        int len;
        long last_active;                                       //记录每次加入红黑树 g_efd 的时间值
    };
    
    int g_efd;                                                  //全局变量, 保存epoll_create返回的文件描述符
    struct myevent_s g_events[MAX_EVENTS+1];                    //自定义结构体类型数组. +1-->listen fd
    
    
    /*将结构体 myevent_s 成员变量 初始化*/
    
    void eventset(struct myevent_s *ev, int fd, void (*call_back)(int, int, void *), void *arg)
    { 
        ev->fd = fd;
        ev->call_back = call_back;
        ev->events = 0;
        ev->arg = arg;                      //思考,为什么要指向自己
        ev->status = 0;
        //memset(ev->buf, 0, sizeof(ev->buf));
        //ev->len = 0;
        ev->last_active = time(NULL);    //调用eventset函数的时间
    
        return;
    }
    
    /* 向 epoll监听的红黑树 添加一个 文件描述符 */
    
    void eventadd(int efd, int events, struct myevent_s *ev)
    { 
        struct epoll_event epv = { 0, { 0}};
        int op;
        epv.data.ptr = ev;
        epv.events = ev->events = events;       //EPOLLIN 或 EPOLLOUT
    
        if (ev->status == 1) {                                           //已经在红黑树 g_efd 里
            op = EPOLL_CTL_MOD;                                         //修改其属性
        } else {                                 //不在红黑树里
            op = EPOLL_CTL_ADD;                 //将其加入红黑树 g_efd, 并将status置1
            ev->status = 1;
        }
    
        if (epoll_ctl(efd, op, ev->fd, &epv) < 0)                       //实际添加/修改
            printf("event add failed [fd=%d], events[%d]\n", ev->fd, events);
        else
            printf("event add OK [fd=%d], op=%d, events[%0X]\n", ev->fd, op, events);
    
        return ;
    }
    
    /* 从epoll 监听的 红黑树中删除一个 文件描述符*/
    
    void eventdel(int efd, struct myevent_s *ev)
    { 
        struct epoll_event epv = { 0, { 0}};
    
        if (ev->status != 1)                                        //不在红黑树上
            return ;
    
        epv.data.ptr = ev;
        ev->status = 0;                                             //修改状态
        epoll_ctl(efd, EPOLL_CTL_DEL, ev->fd, &epv);                //从红黑树 efd 上将 ev->fd 摘除
    
        return ;
    }
    
    /* 当有文件描述符就绪, epoll返回, 调用该函数 与客户端建立链接 */
    // 回调函数 - 监听的文件描述符发送读事件时被调用
    void acceptconn(int lfd, int events, void *arg)
    { 
        struct sockaddr_in cin;
        socklen_t len = sizeof(cin);
        int cfd, i;
    
        if ((cfd = accept(lfd, (struct sockaddr *)&cin, &len)) == -1) { 
            if (errno != EAGAIN && errno != EINTR) { 
                /* 暂时不做出错处理 */
            }
            printf("%s: accept, %s\n", __func__, strerror(errno));
            return ;
        }
    
        do { 
            for (i = 0; i < MAX_EVENTS; i++)                                //从全局数组g_events中找一个空闲元素
                if (g_events[i].status == 0)                                //类似于select中找值为-1的元素
                    break;                                                  //跳出 for
    
            if (i == MAX_EVENTS) { 
                printf("%s: max connect limit[%d]\n", __func__, MAX_EVENTS);
                break;                                                      //跳出do while(0) 不执行后续代码
            }
    
            int flag = 0;
            if ((flag = fcntl(cfd, F_SETFL, O_NONBLOCK)) < 0) {              //将cfd也设置为非阻塞
                printf("%s: fcntl nonblocking failed, %s\n", __func__, strerror(errno));
                break;
            }
    
            /* 给cfd设置一个 myevent_s 结构体, 回调函数 设置为 recvdata */
    
            eventset(&g_events[i], cfd, recvdata, &g_events[i]);   
            eventadd(g_efd, EPOLLIN, &g_events[i]);                         //将cfd添加到红黑树g_efd中,监听读事件
    
        } while(0);
    
        printf("new connect [%s:%d][time:%ld], pos[%d]\n", 
                inet_ntoa(cin.sin_addr), ntohs(cin.sin_port), g_events[i].last_active, i);
        return ;
    }
    
    // 回调函数 - 通信的文件描述符发生读事件时候被调用
    void recvdata(int fd, int events, void *arg)
    { 
        struct myevent_s *ev = (struct myevent_s *)arg;
        int len;
    
        len = recv(fd, ev->buf, sizeof(ev->buf), 0);            //读文件描述符, 数据存入myevent_s成员buf中
    
        eventdel(g_efd, ev);        //将该节点从红黑树上摘除
    
        if (len > 0) { 
    
            ev->len = len;
            ev->buf[len] = '\0';                                //手动添加字符串结束标记
            printf("C[%d]:%s\n", fd, ev->buf);
    
            eventset(ev, fd, senddata, ev);                     //设置该 fd 对应的回调函数为 senddata
            eventadd(g_efd, EPOLLOUT, ev);                      //将fd加入红黑树g_efd中,监听其写事件
    
        } else if (len == 0) { 
            close(ev->fd);
            /* ev-g_events 地址相减得到偏移元素位置 */
            printf("[fd=%d] pos[%ld], closed\n", fd, ev-g_events);
        } else { 
            close(ev->fd);
            printf("recv[fd=%d] error[%d]:%s\n", fd, errno, strerror(errno));
        }
    
        return;
    }
    
    // 回调函数 - 通信的文件描述符发生写事件时候被调用
    void senddata(int fd, int events, void *arg)
    { 
        struct myevent_s *ev = (struct myevent_s *)arg;
        int len;
    
        len = send(fd, ev->buf, ev->len, 0);                    //直接将数据 回写给客户端。未作处理
        /* printf("fd=%d\tev->buf=%s\ttev->len=%d\n", fd, ev->buf, ev->len); printf("send len = %d\n", len); */
    
        if (len > 0) { 
    
            printf("send[fd=%d], [%d]%s\n", fd, len, ev->buf);
            eventdel(g_efd, ev);                                //从红黑树g_efd中移除
            eventset(ev, fd, recvdata, ev);                     //将该fd的 回调函数改为 recvdata
            eventadd(g_efd, EPOLLIN, ev);                       //从新添加到红黑树上， 设为监听读事件
    
        } else { 
            close(ev->fd);                                      //关闭链接
            eventdel(g_efd, ev);                                //从红黑树g_efd中移除
            printf("send[fd=%d] error %s\n", fd, strerror(errno));
        }
    
        return ;
    }
    
    /*创建 socket, 初始化lfd */
    
    void initlistensocket(int efd, short port)
    { 
        int lfd = socket(AF_INET, SOCK_STREAM, 0);
        fcntl(lfd, F_SETFL, O_NONBLOCK);                                            //将socket设为非阻塞
    
        /* void eventset(struct myevent_s *ev, int fd, void (*call_back)(int, int, void *), void *arg); */
        eventset(&g_events[MAX_EVENTS], lfd, acceptconn, &g_events[MAX_EVENTS]);
    
        /* void eventadd(int efd, int events, struct myevent_s *ev) */
        eventadd(efd, EPOLLIN, &g_events[MAX_EVENTS]);
    
        struct sockaddr_in sin;
    	memset(&sin, 0, sizeof(sin));                                               //bzero(&sin, sizeof(sin))
    	sin.sin_family = AF_INET;
    	sin.sin_addr.s_addr = INADDR_ANY;
    	sin.sin_port = htons(port);
    
    	bind(lfd, (struct sockaddr *)&sin, sizeof(sin));
    
    	listen(lfd, 20);
    
        return ;
    }
    
    int main(int argc, char *argv[])
    { 
        unsigned short port = SERV_PORT;
    
        if (argc == 2)
            port = atoi(argv[1]);                           //使用用户指定端口.如未指定,用默认端口
    
        g_efd = epoll_create(MAX_EVENTS+1);                 //创建红黑树,返回给全局 g_efd 
        if (g_efd <= 0)
            printf("create efd in %s err %s\n", __func__, strerror(errno));
    
        initlistensocket(g_efd, port);                      //初始化监听socket
    
        struct epoll_event events[MAX_EVENTS+1];            //保存已经满足就绪事件的文件描述符数组 
    	printf("server running:port[%d]\n", port);
    
        int checkpos = 0, i;
        while (1) { 
            /* 超时验证，每次测试100个链接，不测试listenfd 当客户端60秒内没有和服务器通信，则关闭此客户端链接 */
    
            long now = time(NULL);                          //当前时间
            for (i = 0; i < 100; i++, checkpos++) {          //一次循环检测100个。 使用checkpos控制检测对象
                if (checkpos == MAX_EVENTS)
                    checkpos = 0;
                if (g_events[checkpos].status != 1)         //不在红黑树 g_efd 上
                    continue;
    
                long duration = now - g_events[checkpos].last_active;       //客户端不活跃的世间
    
                if (duration >= 60) { 
                    close(g_events[checkpos].fd);                           //关闭与该客户端链接
                    printf("[fd=%d] timeout\n", g_events[checkpos].fd);
                    eventdel(g_efd, &g_events[checkpos]);                   //将该客户端 从红黑树 g_efd移除
                }
            }
    
            /*监听红黑树g_efd, 将满足的事件的文件描述符加至events数组中, 1秒没有事件满足, 返回 0*/
            int nfd = epoll_wait(g_efd, events, MAX_EVENTS+1, 1000);
            if (nfd < 0) { 
                printf("epoll_wait error, exit\n");
                break;
            }
    
            for (i = 0; i < nfd; i++) { 
                /*使用自定义结构体myevent_s类型指针, 接收 联合体data的void *ptr成员*/
                struct myevent_s *ev = (struct myevent_s *)events[i].data.ptr;  
    
                if ((events[i].events & EPOLLIN) && (ev->events & EPOLLIN)) {            //读就绪事件
                    ev->call_back(ev->fd, events[i].events, ev->arg);
                }
                if ((events[i].events & EPOLLOUT) && (ev->events & EPOLLOUT)) {          //写就绪事件
                    ev->call_back(ev->fd, events[i].events, ev->arg);
                }
            }
        }
    
        /* 退出前释放所有资源 */
        return 0;
    }

[linux_epoll]: https://blog.csdn.net/e891377/article/details/108202512
[20200828194209193.jpg]: /images/20221123/73d4ec046cd744bd870898e404e58f99.png